More radio stuff

teejk · Sep 21, 2016

I will apologize in advance for not searching/appending older threads on this topic. I find that I listen to much more radio now than I watch TV. Just me. So here's my story. I have a metal shop building (inside and out). I have 2 long strips (24' each) of T8 fluorescent lights on separate switches spaced 10' apart and 10' from each sidewall. FM signals were easy with a simple external wire outside the shop. AM was always "iffy" depending on weather but for a few years my Milwaukee job site radio would work with its internal AM antenna. Might have been a voltage spike or something but it stopped performing on AM. So I bought a good AM/FM external "spike" antenna and mounted it on a 16' mast outside the shop. The tip extends well above the metal shop roof line and the mast itself sits about a foot away from the building. Single RG6 cable that comes into the building and connects to a splitter (supplied by the antenna people) inside the building. Also bought a new receiver (Pyle Audio). That unfortunately had the antenna connections with those little spring loaded clips that require a coax to twin lead adaptor on both the AM and FM sides. I can get pretty good reception on the FM (other than that adaptor can be fussy). The AM side though is giving me problems. The leads on the adaptor are maybe 22ga wire and if I "fiddle" with it the signal will go from "ok" to "nothing" so I suspect the problem lies with that adaptor and/or how it works with the receiver. I have tried both vanilla and quad shield cable. I'll leave the question at that for now.

Industrial Toys · Sep 21, 2016

I kind of lost you. But the important thing is that the impedance is maintained. Or a matching transformer is used if the impedance is changed. The RG 6 is 75 ohm and I hope the antenna is as well. The terminals on the radio are probably 300 ohm (balanced) and would need a transformer to match to 75 ohm. The manual should tell you the input specs.

I would probably think about a lightning arrestor as well.

teejk · Sep 22, 2016

Thanks. I checked the receiver manual and don't see any input specs. The antenna (DX Engineering) instructions show things exactly as I described RG6 from antenna to splitter, one coax to a F to twin lead adaptor (supplied) to the AM antenna terminals, another coax to a separate twin lead adaptor that I purchased locally (antenna mfgr assumed a coax input for FM). I think the problem lies in the supplied twin lead adaptor. Pretty thin wire compared to the size of the antenna inputs and if I "fiddle" with it, it seems to work but seems to be very fussy in how it is positioned. Guess I'll contact the receiver maker and see if they have any ideas. Barring that maybe I'll hit the leads with a bit of silver solder to give them some structure.

dickfoster · Sep 22, 2016

teejk said:
I will apologize in advance for not searching/appending older threads on this topic. I find that I listen to much more radio now than I watch TV. Just me. So here's my story. I have a metal shop building (inside and out). I have 2 long strips (24' each) of T8 fluorescent lights on separate switches spaced 10' apart and 10' from each sidewall. FM signals were easy with a simple external wire outside the shop. AM was always "iffy" depending on weather but for a few years my Milwaukee job site radio would work with its internal AM antenna. Might have been a voltage spike or something but it stopped performing on AM. So I bought a good AM/FM external "spike" antenna and mounted it on a 16' mast outside the shop. The tip extends well above the metal shop roof line and the mast itself sits about a foot away from the building. Single RG6 cable that comes into the building and connects to a splitter (supplied by the antenna people) inside the building. Also bought a new receiver (Pyle Audio). That unfortunately had the antenna connections with those little spring loaded clips that require a coax to twin lead adaptor on both the AM and FM sides. I can get pretty good reception on the FM (other than that adaptor can be fussy). The AM side though is giving me problems. The leads on the adaptor are maybe 22ga wire and if I "fiddle" with it the signal will go from "ok" to "nothing" so I suspect the problem lies with that adaptor and/or how it works with the receiver. I have tried both vanilla and quad shield cable. I'll leave the question at that for now.

Just so you know the frequency is very different for FM and AM radio signals. Antennas are made to perform within a certain range of frequencies so one made for FM will provide crappy performance for AM and vice versa. It doesn't matter what the manufacture claims because it's dictated by the laws of physics. FM signals are also horizontally polarized and line of sight signals while AM is mostly vertical and a ground wave signal. Often a long hunk of wire strung up will do the job for an AM receiver. Due to the popularity of FM and it's improved noise performance, stereo etc, later day AM radios just aren't what they used to be. Most makers just throw something in there to put AM on the label but do little to optimise the design or performance for AM. Older AM radios will typically outperform later units by a wide margin.
You could try one of these
Tecsun AN-1 Tunable AM/MW Antenna (No Battery/No Antenna Jack Needed) | eBay
made specifically for AM but you'd likely be better off with an external long wire for your AM radio. Run the wire out far enough then run it up or down a tree or something to get the best AM reception.
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/radio.html

teejk · Sep 22, 2016

dickfoster said:
Just so you know the frequency is very different for FM and AM radio signals. Antennas are made to perform within a certain range of frequencies so one made for FM will provide crappy performance for AM and vice versa. It doesn't matter what the manufacture claims because it's dictated by the laws of physics. FM signals are also horizontally polarized and line of sight signals while AM is mostly vertical and a ground wave signal. Often a long hunk of wire strung up will do the job for an AM receiver. Due to the popularity of FM and it's improved noise performance, stereo etc, later day AM radios just aren't what they used to be. Most makers just throw something in there to put AM on the label but do little to optimise the design or performance for AM. Older AM radios will typically outperform later units by a wide margin.
You could try one of these
Tecsun AN-1 Tunable AM/MW Antenna (No Battery/No Antenna Jack Needed) | eBay
made specifically for AM but you'd likely be better off with an external long wire for your AM radio. Run the wire out far enough then run it up or down a tree or something to get the best AM reception.
http://hyperphysics.phy-astr.gsu.edu/hbase/audio/radio.html

Thanks for the info. The antenna I bought (DXE-AFHD-4) tested for 80 miles on FM, 90 miles on AM. "Fiddled" around some more today and found that the sound was great (AM/FM) if I DIDN'T connect the negative leg of the twin lead adaptors to the negative antenna ports on the receiver. My shop is metal inside and out and my electrical runs are flush mounted EMT with 2 duplex outlets mounted every 10' where the EMT also serves as the grounding system. I've checked for potential "stray"voltage everywhere and have found none. I mounted the splitter inside the building since I already had my "red-neck" wire loop outside for my old receiver and used the existing outside RG6 for that. Time to contact both the antenna guys and the receiver guys I guess. Connecting those tiny ground wires to the back of the receiver and losing the signal tells me that something ain't right.

Oaktree · Sep 22, 2016

dickfoster said:
FM signals are also horizontally polarized and line of sight signals

Actually, most FM signals are circularly polarized and will work with either vertical or horizontal antennas.

PILOON · Sep 22, 2016

Most effective antennas are 1/4, 1/2 or full wave length and there are formulas to calculate that.
For FM you are near TV low band so often a splitter works here.
For AM generally a long wire works if oriented properly. (like spread your arms facing the station)

teejk · Sep 22, 2016

PILOON said:
Most effective antennas are 1/4, 1/2 or full wave length and there are formulas to calculate that.
For FM you are near TV low band so often a splitter works here.
For AM generally a long wire works if oriented properly. (like spread your arms facing the station)

Glad to get some input on this...but here's the specs on the antenna (all wasted on me because I was an accountant in a previous life)...Antenna length 48"...Antenna beam width Omni-directional...AM capture length 300 inches...Ground plane required None...AM/FM band separator FM rejection on AM band >50 dB...AM rejection in FM band >60 dB AM/FM....Pass-band loss: <1 dB load impedance :300 ohms...FM load impedance 75 ohms. That is the antenna I bought. It came with the splitter and a coax to twin lead adaptor that according to their diagram went to the AM connections (red to +, black to -). As noted above, everything works great IF I leave that black wire out. Based on the above, guessing that supplied adaptor somehow converts from 75ohms to 300 ohms (or perhaps that is in the splitter) but again I don't understand any of this stuff.

Industrial Toys · Sep 22, 2016

My newer expensive vapor tight flourescent lights in my wood shed cause me RFI. Also a structural steel building. I bought the same ones for a friends shop and we ordered (and paid for) premium ballasts. They were still noisy, so my friend in the elect. dist. bus. got us new ballasts and we changed them all out. Nice and quiet now. I should change mine too.

If the RFI is so great as to desensitize the receiver, no practical antenna will solve the problem.

And, as far as antenna distance specs go. That assumes a (mostly) clear line of sight. EDITED, Meaning FM (of course) VHF being the limiting factor, not the modulation.

k0ua · Sep 22, 2016

I would be extremely concerned if I could only receive AM broadcast band signals up to 90 miles away.

At least at night you should be able to receive signals from at least several hundred to several thousands of miles.

Even during the day time you should be able to receive the 50 Kilowatt clear channel stations a couple of hundred miles away at least.

I am always amused by manufacturers placing a number on how far you can receive a signal on their antenna's. But people ask such questions. There is no correct milage answer. The correct answer is "it depends" FM broadcast band (88-108 MHz) can easily propagate for several thousands of miles via one of many different propagation modes. E layer propagation is very common. AM broadcast band signals can easily propagate all the way around the earth under some conditions. During grey line conditions where the terminator is near your location and the transmitting stations location, it is possible to receive a signal both long path and short path. Yes that is right, a signal that has went all the way one direction around the earth and a corresponding signal that has taken a shorter path partially around the earth to your location. I have personally "worked" amateur radio stations with simultaneous long path and short path signals. It makes for an interesting "echo" to hear the long path signal come in a fraction of a second after the short path signal arrives.

Yes, I know the "estimates" that manufactures publish on Antennas are figures for "average" ground wave propagation modes with some sort of "average" installation with some sort of "average" receiver, with some sort of "average" local noise level. As if there was actually some sort of thing as "average".

But people want simple answers to very complex questions. Like "how far can you talk on that thing?" There is no simple answer. So Manufactures will make one up.